The subject matter described herein relates mainly to toner and developer compositions, and more specifically, to toner and developer compositions that are made to have particles, preferably spacer particles, attached firmly to the toner particle surface. Also described is a method of firmly attaching such surface particles to the surface of the toner particles in-situ (i.e., during formation of the toner particles).
The use of spacer particles upon the surface of toner particles is known in the art. Spacers can be employed for a number of reasons in that the spacers typically decrease toner particle adhesion and cohesion. The spacers can improve toner flow, charging, development and transfer during the xerographic process. A particular advantage associated with the use of spacer particles upon the toner particle surface is that the spacer particles act to protect the toner particles from the high amount of abuse the toner particles receive in the developer housing. In the developer housing, the toner particles are constantly impacted by other toner particles and by carrier particles. Such impaction can, over time, embed smaller surface additives, change the charging properties, and thus the transfer quality, of the toner particles. One theory is that this reduction in performance over time is due to the impaction of small conventional toner surface additives of, for example, a size of from about 5 to about 40 nanometers, such as silica, titania and zinc stearate, during aging in the development housing. The presence of spacers can thus reduce such impaction and the negative effects associated therewith.
U.S. Pat. No. 5,763,132, incorporated herein by reference in its entirety, describes a process for decreasing toner adhesion and decreasing toner cohesion, which comprises adding a hard spacer component of a polymer of polymethyl methacrylate (PMMA), a metal, a metal oxide, a metal carbide, or a metal nitride, to the surface of a toner comprised of resin, wax, compatibilizer, and colorant excluding black, and wherein toner surface additives are blended with said toner, and wherein said component is permanently attached to the toner surface by the injection of said component in a fluid bed milling device during the size reduction process of said toner contained in said device, and where the power imparted to the toner to obtain said attachment is from equal to, or about above, 5 watts per gram of toner. See the Abstract and column 1, lines 9-28.
U.S. Pat. No. 5,716,752, incorporated herein by reference in its entirety, similarly describes a process for decreasing toner adhesion and decreasing toner cohesion, which comprises adding a component of magnetite, a metal, a metal oxide, a metal carbide, or a metal nitride to the surface of a toner comprised of resin, wax, and colorant, and wherein toner surface additives are blended with said toner, and wherein said component is permanently attached to the toner surface by the injection of said component in a fluid bed milling device during the size reduction process of said toner contained in said device, and where the power imparted to the toner to obtain said attachment is from equal to, or about above, 5 watts per gram of toner. See the Abstract.
Thus, although the use of spacer particles upon the surface of toner particles is known, such spacer particles are typically hard particles that are attached to the toner particle surface by mechanical means such as fluid bed or jet milling. Both of the aforementioned references require that the spacers described therein be attached to the toner particles with high power injection in a fluid bed milling device during the size reduction (grinding) step, thereby requiring the use of hard spacer particles. Softer spacer type particles thus cannot be used in such attachment methods as they would be crushed or buried into the toner particles, and thus rendered ineffective for their intended purpose.
Recently, ultra large spacer particles, e.g., having a size of about 140 nm, have been added to a toner particle surface in a normal toner blending step. For example, after addition of smaller size additives by inject at grind as discussed above, such larger additives are added in a subsequent gentler toner blending process that is much less abusive than inject at grind. However, although this blending step is less abusive than the inject at grind procedure discussed above, the larger additives are not strongly adhered to the toner and can readily flake off and interfere with the quality of the image developed.